[rtorrent] Fixed naming issue

Not sure how this bug got into here, this function is referenced at [rtorrent/main.py#L139](https://github.com/fuzeman/CouchPotatoServer/blob/9056f5ae59dfde6a479d2b962b869647043f9ba3/couchpotato/core/downloaders/rtorrent/main.py#L139) but under the correct name.